Radial keratotomy is a surgical method that consists of forming incisions of a desired depth and location on the surface of the cornea to change the curvature of the cornea. This operation is used to correct myopia and other defects which relate to the curvature of the cornea. Although it has been suggested that radial keratotomy works by peripheral bulging of the cornea, the more accepted view is that the effect is due to the entire cornea stretching. After radial keratotomy, the cornea is weakened by the incisions therein and the intraocular pressure stretches the cornea, with most of the stretching occurring near the optical zone. The stretching increases the radius of curvature of the cornea, thereby flattening the cornea and improving the vision of the patient. The deeper the incisions made during the operation and the smaller the optical zone the more the cornea will stretch. Deepening the incisions near the limbus will increase the effect, but deepening the incisions near the optical zone will have a greater effect. The maximum effect is achieved if the incisions are at maximal depth. It is thus important to carefully monitor the incisions and the resulting changes in the cornea to insure a successful operation.
A keratometer is currently used to determine the radius of curvature of the cornea and thereby calculate the optical power of the cornea. During the performance of radial keratotomy, however, the corneal stroma swells because of corneal edema which is caused by the incisions through the epithelium. This edema is only temporary and will dissipate as the cornea heals (approximately 2-6 months). As a result, any measurement of the radius of curvature of the anterior surface of the cornea during the operation or in the immediate postoperative period will not be correct in predicting the final outcome of the surgery. Thus, one must wait months before the full effects of radial keratotomy can be measured using currently available methods. A need exists, therefore, for a method and apparatus for measuring the intraoperative and immediate postoperative effects of radial keratotomy to enable one to immediately predict the effects (i.e., the change in the radius of curvature of the anterior surface of the cornea) of the surgery.